The number of users in wireless communication networks is constantly increasing. Also the number of different services being offered by the various wireless communication networks is constantly increasing. In order to cope with increasing demand on e.g. capacity and speed of the networks, different technologies and so called generations of the wireless communication networks have been developed. Today, it is relatively common to have several generations of wireless communication networks overlapping and operating simultaneously. For example, there may be a 2G communication network such as Global System for Mobile communication, GSM, and a 3G communication network such as Universal Mobile Telecommunications System, UMTS, together with a 4G communication network such as Long Term Evolution, LTE, more or less overlapping. Many wireless devices, hereinafter referred to as UEs, such as e.g. mobile telephones, laptops, personal digital assistants, and other devices having means for communicating wirelessly with a wireless communication network, may be operated on some or all of the above mentioned wireless communication networks, 2G, 3G and 4G.
The different wireless networks are more or less suitable for different services being offered by the wireless communication networks. Merely as an example, 2G is most suitable for speech calls, whereas 3G is suitable both for speech calls and data transfer and 4G having a much higher bitrate is even more suitable than 3G for transferring data. Thus, a UE may be handed over between the different communication networks both with regard to which wireless communication networks are available and with regard to which service(s) the UE is engaged in.
Since the different wireless communication networks, 2G, 3G and 4G, are based on different technologies, several problems may arise when a UE is to be handed over from one network, e.g. a 3G network, to another network, e.g. a 4G network.